A combination of two major factors. First off is the major pre-order backlash that's growing, which was further fueled this year by disappointing releases like Deus Ex: Mankind Divided, No Man's Sky, Street Fighter V, and others I'm sure I'm forgetting. The other factor is the Amazon Prime 20% discount for pre-orders AND newly released (within 2 weeks) games. Yes, that's right -- I can NOT pre-order, wait for the reviews to come out, then decide a week later, and STILL pay 20% than someone who ordered from GameStop. There's no drawbacks because the chance they'll "out of stock" (Ha! in this digital age?) is pretty unlikely because they're Amazon. So, unless I'm some fiddly obsessive who cares about collecting the special pre-order skins or starter gear that won't even matter after level 6, why would I pre-order from GameStop?